The long term objective of the project is to understand the bone matrix collagen assembly, specifically the role of type V collagen in bone matrix. There is a growing body of evidence indicating that collagen- collagen interactions may play an important role in controlling fiber diameter and also in providing fibril network with reinforcement, thereby specifying the mechanical properties of different tissues. Although a lot of information has been gathered on type V collagen, its function in bone or other tissues remains poorly understood. Three approaches will be explored for understanding the role of type V collagen in bone matrix. The first will be to determine the potential of type V collagen to copolymerize with type 1 collagen by analysis of the nature of intermolecular cross-linking in bone type V collagen. Secondly, to determine the role of the retained extension peptides on the tissue form of type V collagen, and thirdly to assess the mode of type V collagen degradation. All the intermolecular cross-linking sites in bone type V collagen involving sodium borohydride reducible cross-links and also those involving the mature 3-hydroxypyridinolines will be determined. The reducible cross-links in type V collagen will be determined after reacting the collagen with tritiated sodium borohydride to label the cross-linking bonds. Cross-linked peptides involving 3-hydroxypyridinium residues in type V collagen will be followed by their fluorescence, purified and subjected to protein microsequencing analysis. The role of the extension peptides retained on the tissue form of type V collagen will be assessed by generating the extension peptides from the alpha chains by bacterial collagenase digestion and then producing monospecific antibodies against the extension peptides. The generated antibodies will then be used to examine the role of these extension peptides in bone collagen fibrils. The mode of type V collagen degradation by type V collagenase will be determined by incubating native type V collagen with type V collagenase. The initial sites of attack within the type V collagen will be determined by aminoterminal sequence analysis of the generated fragments. Understanding the bone matrix collagen assembly may help to explain how increased ratio of type V to type I collagen in osteogenesis imperfecta patients may impair structural integrity of the bone tissue and contribute to mechanical weakness.